1. © 2005 Pearson Education Inc., publishing as Addison-Wesley Chapter 3 The Science of Astronomy

2. © 2005 Pearson Education Inc., publishing as Addison-Wesley 3.1 The Ancient Roots of Science In what ways do all humans employ scientific thinking? How did astronomical observations benefit ancient societies? What did ancient civilizations achieve in astronomy? Our goals for learning:

3. © 2005 Pearson Education Inc., publishing as Addison-Wesley In what ways do all humans employ scientific thinking? Scientific thinking is based on everyday ideas of observation and trial-and-error experiments.

4. © 2005 Pearson Education Inc., publishing as Addison-Wesley How did astronomical observations benefit ancient societies? Keeping track of time and seasons – for practical purposes, including agriculture – for religious and ceremonial purposes Aid to navigation

5. © 2005 Pearson Education Inc., publishing as Addison-Wesley Ancient people of central Africa (6500 BC) could predict seasons from the orientation of the crescent moon

6. © 2005 Pearson Education Inc., publishing as Addison-Wesley Days of week were named for Sun, Moon, and visible planets

7. © 2005 Pearson Education Inc., publishing as Addison-Wesley What did ancient civilizations achieve in astronomy? daily timekeeping tracking the seasons and calendar monitoring lunar cycles monitoring planets and stars predicting eclipses and more…

8. © 2005 Pearson Education Inc., publishing as Addison-Wesley Egyptian obelisk: shadows tell time of day.

9. © 2005 Pearson Education Inc., publishing as Addison-Wesley England: Stonehenge (completed around 1550 B.C.)

10. © 2005 Pearson Education Inc., publishing as Addison-Wesley England: Stonehenge (1550 B.C.)

11. © 2005 Pearson Education Inc., publishing as Addison-Wesley Mexico: model of the Templo Mayor

12. © 2005 Pearson Education Inc., publishing as Addison-Wesley SW United States: “Sun Dagger” marks summer solstice

13. © 2005 Pearson Education Inc., publishing as Addison-Wesley Scotland: 4,000-year-old stone circle; Moon rises as shown here every 18.6 years.

14. © 2005 Pearson Education Inc., publishing as Addison-Wesley Yucatan, Mexico: Mayan Observatory at Chichen Itza

15. © 2005 Pearson Education Inc., publishing as Addison-Wesley Peru: lines and patterns, some aligned with stars.

16. © 2005 Pearson Education Inc., publishing as Addison-Wesley Wyoming: Big Horn Medicine Wheel

17. © 2005 Pearson Education Inc., publishing as Addison-Wesley South Pacific: Polynesians were very skilled in art of celestial navigation

18. © 2005 Pearson Education Inc., publishing as Addison-Wesley France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots)

19. © 2005 Pearson Education Inc., publishing as Addison-Wesley China: Earliest known records of supernova explosions (1400 B.C.) Bone or tortoise shell inscription from the 14th century BC. "On the Xinwei day the new star dwindled." "On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star."

20. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? In what ways do all humans employ scientific thinking? –Scientific thinking involves the same type of trial and error thinking that we use in our everyday lives, but in a carefully organized way How did astronomical observations benefit ancient societies? –Keeping track of time and seasons; navigation

21. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? What did ancient civilizations achieve in astronomy? –Tell the time of day and year, to track cycles of the Moon, to observe planets and stars. Many ancient structures aided in astronomical observations.

22. © 2005 Pearson Education Inc., publishing as Addison-Wesley 3.2 Ancient Greek Science Why does modern science trace its roots to the Greeks? How did the Greeks explain planetary motion? How did Islamic scientists preserve and extend Greek science? Our goals for learning:

23. © 2005 Pearson Education Inc., publishing as Addison-Wesley Our mathematical and scientific heritage originated with the civilizations of the Middle East

24. © 2005 Pearson Education Inc., publishing as Addison-Wesley Artist’s reconstruction of Library of Alexandria

25. © 2005 Pearson Education Inc., publishing as Addison-Wesley Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural. Greek geocentric model (c. 400 BC) Why does modern science trace its roots to the Greeks?

26. © 2005 Pearson Education Inc., publishing as Addison-Wesley Special Topic: Eratosthenes measures the Earth (c. 240 BC) Calculate circumference of Earth: 7/360  (circum. Earth) = 5000 stadia  circum. Earth = 5000  360/7 stadia ≈ 250,000 stadia Measurements: Syene to Alexandria distance ≈ 5000 stadia angle = 7° Compare to modern value (≈ 40,100 km): Greek stadium ≈ 1/6 km  250,000 stadia ≈ 42,000 km

27. © 2005 Pearson Education Inc., publishing as Addison-Wesley Underpinnings of the Greek geocentric model: Plato Aristotle How did the Greeks explain planetary motion? Earth at the center of the universe Heavens must be “perfect” : objects moving on perfect spheres or in perfect circles.

28. © 2005 Pearson Education Inc., publishing as Addison-Wesley But this made it difficult to explain apparent retrograde motion of planets… Review: Over a period of 10 weeks, Mars appears to stop, back up, then go forward again.

29. © 2005 Pearson Education Inc., publishing as Addison-Wesley The most sophisticated geocentric model was that of Ptolemy (A.D. 100-170) — the Ptolemaic model: Sufficiently accurate to remain in use for 1,500 years. Arabic translation of Ptolemy’s work named Almagest (“the greatest compilation”) Ptolemy

30. © 2005 Pearson Education Inc., publishing as Addison-Wesley So how does the Ptolemaic model explain retrograde motion? Planets really do go backward in this model..

31. © 2005 Pearson Education Inc., publishing as Addison-Wesley Thought Question Which of the following is NOT a fundamental difference between the geocentric and Sun-centered models of the solar system? A.Earth is stationary in the geocentric model but moves around Sun in Sun-centered model. B.Retrograde motion is real (planets really go backward) in geocentric model but only apparent (planets don’t really turn around) in Sun- centered model. C.Stellar parallax is expected in the Sun-centered model but not in the Earth-centered model. D.The geocentric model is useless for predicting planetary positions in the sky, while even the earliest Sun-centered models worked almost perfectly.

32. © 2005 Pearson Education Inc., publishing as Addison-Wesley Which of the following is NOT a fundamental difference between the geocentric and Sun-centered models of the solar system? A.Earth is stationary in the geocentric model but moves around Sun in Sun-centered model. B.Retrograde motion is real (planets really go backward) in geocentric model but only apparent (planets don’t really turn around) in Sun- centered model. C.Stellar parallax is expected in the Sun-centered model but not in the Earth-centered model. D.The geocentric model is useless for predicting planetary positions in the sky, while even the earliest Sun-centered models worked almost perfectly.

33. © 2005 Pearson Education Inc., publishing as Addison-Wesley How did Islamic scientists preserve and extend Greek science? Muslim world preserved and enhanced the knowledge they received from the Greeks Al-Mamun’s House of Wisdom in Baghdad was a great center of learning around A.D. 800 With the fall of Constantinople (Istanbul) in 1453, Eastern scholars headed west to Europe, carrying knowledge that helped ignite the European Renaissance.

34. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? Why does modern science trace its roots to the Greeks? They developed models of nature and emphasized that the predictions of models should agree with observations. How did the Greeks explain planetary motion? The Ptolemaic model had each planet move on a small circle whose center moves around Earth on a larger circle.

35. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? How did Islamic scientists preserve and extend Greek science? While Europe was in its Dark Ages, Islamic scientists preserved and extended Greek science, later helping to ignite the European Renaissance.

36. © 2005 Pearson Education Inc., publishing as Addison-Wesley 3.3 The Copernican Revolution How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea? What are Kepler’s three laws of planetary motion? How did Galileo solidify the Copernican revolution? Our goals for learning:

37. © 2005 Pearson Education Inc., publishing as Addison-Wesley How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea? Copernicus (1473-1543): proposed Sun-centered model (published 1543) used model to determine layout of solar system (planetary distances in AU) But... model was no more accurate than Ptolemaic model in predicting planetary positions, because still used perfect circles.

38. © 2005 Pearson Education Inc., publishing as Addison-Wesley Tycho Brahe (1546-1601) Compiled the most accurate (one arcminute) naked eye measurements ever made of planetary positions. Still could not detect stellar parallax, and thus still thought Earth must be at center of solar system (but recognized that other planets go around Sun) Hired Kepler, who used his observations to discover the truth about planetary motion.

39. © 2005 Pearson Education Inc., publishing as Addison-Wesley Johannes Kepler (1571-1630) Kepler first tried to match Tycho’s observations with circular orbits But an 8 arcminute discrepancy led him eventually to ellipses… If I had believed that we could ignore these eight minutes [of arc], I would have patched up my hypothesis accordingly. But, since it was not permissible to ignore, those eight minutes pointed the road to a complete reformation in astronomy.

40. © 2005 Pearson Education Inc., publishing as Addison-Wesley An ellipse looks like an elongated circle What is an Ellipse?

41. © 2005 Pearson Education Inc., publishing as Addison-Wesley Eccentricity of an Ellipse

42. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus. What are Kepler’s three laws of planetary motion?

43. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times.  means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

44. © 2005 Pearson Education Inc., publishing as Addison-Wesley

45. More distant planets orbit the Sun at slower average speeds, obeying the relationship p 2 = a 3 p = orbital period in years a = avg. distance from Sun in AU Kepler’s Third Law

46. © 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 3 rd Law

47. © 2005 Pearson Education Inc., publishing as Addison-Wesley Graphical version of Kepler’s Third Law

48. © 2005 Pearson Education Inc., publishing as Addison-Wesley Thought Question: An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.4 years B.8 years C.16 years D.64 years Hint: Remember that p 2 = a 3

49. © 2005 Pearson Education Inc., publishing as Addison-Wesley An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.4 years B.8 years C.16 years D.64 years We need to find p so that p 2 = a 3 Since a = 4, a 3 = 4 3 = 64 Therefore p = 8, p 2 = 8 2 = 64

50. © 2005 Pearson Education Inc., publishing as Addison-Wesley How did Galileo solidify the Copernican revolution? Galileo (1564-1642) overcame major objections to Copernican view. Three key objections rooted in Aristotelian view were: 1.Earth could not be moving because objects in air would be left behind. 2.Non-circular orbits are not “perfect” as heavens should be. 3.If Earth were really orbiting Sun, we’d detect stellar parallax.

51. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo’s experiments showed that objects in air would stay with a moving Earth. Overcoming the first objection (nature of motion): Aristotle thought that all objects naturally come to rest. Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton’s first law of motion).

52. © 2005 Pearson Education Inc., publishing as Addison-Wesley Overcoming the second objection (heavenly perfection): Tycho’s observations of comet and supernova already challenged this idea. Using his telescope, Galileo saw: sunspots on Sun (“imperfections”) mountains and valleys on the Moon (proving it is not a perfect sphere)

53. © 2005 Pearson Education Inc., publishing as Addison-Wesley Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. Galileo showed stars must be much farther than Tycho thought — in part by using his telescope to see the Milky Way is countless individual stars. If stars were much farther away, then lack of detectable parallax was no longer so troubling. Overcoming the third objection (parallax):

54. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit the Earth…

55. © 2005 Pearson Education Inc., publishing as Addison-Wesley … and his observations of phases of Venus proved that it orbits the Sun and not Earth.

56. © 2005 Pearson Education Inc., publishing as Addison-Wesley Galileo Galilei The Catholic Church ordered Galileo to recant his claim that Earth orbits the Sun in 1633 His book on the subject was removed from the Church’s index of banned books in 1824 Galileo was formally vindicated by the Church in 1992

57. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? How did Copernicus, Tycho and Kepler challenge the Earth-centered idea? Copernicus created a sun-centered model; Tycho provided the data needed to improve this model; Kepler found a model that fit Tycho’s data.

58. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? Kepler’s three laws of planetary motion: 1. The orbit of each planet is an ellipse with the Sun at one focus 2. As a planet moves around its orbit it sweeps our equal areas in equal times 3. More distance planets orbit the Sun at slower average speeds: p 2 = a 3 Kepler’s second law

59. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? What was Galileo’s role in the Copernican revolution? His experiments and observations overcame the remaining objections to the Sun-centered solar system

60. © 2005 Pearson Education Inc., publishing as Addison-Wesley 3.4 The Nature of Science How can we distinguish science from nonscience? What is a scientific theory? Our goals for learning:

61. © 2005 Pearson Education Inc., publishing as Addison-Wesley How can we distinguish science from non-science? Defining science can be surprisingly difficult. Science from the Latin scientia, meaning “knowledge.” But not all knowledge comes from science…

62. © 2005 Pearson Education Inc., publishing as Addison-Wesley The idealized scientific method Based on proposing and testing hypotheses hypothesis = educated guess

63. © 2005 Pearson Education Inc., publishing as Addison-Wesley But science rarely proceeds in this idealized way… For example: Sometimes we start by “just looking” then coming up with possible explanations. Sometimes we follow our intuition rather than a particular line of evidence.

64. © 2005 Pearson Education Inc., publishing as Addison-Wesley Hallmarks of Science: #1 Modern science seeks explanations for observed phenomena that rely solely on natural causes. (A scientific model cannot include divine intervention)

65. © 2005 Pearson Education Inc., publishing as Addison-Wesley Hallmarks of Science: #2 Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = “Occam’s razor”)

66. © 2005 Pearson Education Inc., publishing as Addison-Wesley Hallmarks of Science: #3 A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.

67. © 2005 Pearson Education Inc., publishing as Addison-Wesley What is a scientific theory? The word theory has a different meaning in science than in everyday life. In science, a theory is NOT the same as a hypothesis, rather: A scientific theory must: Explain a wide variety of observations with a few simple principles, AND Must be supported by a large, compelling body of evidence. Must NOT have failed any crucial test of its validity.

68. © 2005 Pearson Education Inc., publishing as Addison-Wesley Thought Question Darwin’s theory of evolution meets all the criteria of a scientific theory. This means: A.Scientific opinion is about evenly split as to whether evolution really happened. B.Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed. C.After more than 100 years of putting Darwin’s theory to the test, the theory stands stronger than ever, having successfully met every scientific challenge to its validity. D.There is no longer any doubt that the theory of evolution is absolutely true.

69. © 2005 Pearson Education Inc., publishing as Addison-Wesley Darwin’s theory of evolution meets all the criteria of a scientific theory. This means: A.Scientific opinion is about evenly split as to whether evolution really happened. B.Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed. C.After more than 100 years of putting Darwin’s theory to the test, the theory stands stronger than ever, having successfully met every scientific challenge to its validity. D.There is no longer any doubt that the theory of evolution is absolutely true.

70. © 2005 Pearson Education Inc., publishing as Addison-Wesley What have we learned? How can we distinguish science from non-science? Science: seeks explanations that rely solely on natural causes; progresses through the creation and testing of models of nature; models must make testable predictions What is a scientific theory? A model that explains a wide variety of observations in terms of a few general principles and that has survived repeated and varied testing